[ios] Disable failing multitasking fullscreen test.

Bug: 872788
TBR: rohitrao
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I55e2ba91fe5cbd0ef170d7a34d7e5104b7de735a
Reviewed-on: https://chromium-review.googlesource.com/1169318
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581901}

ios/chrome/test/earl_grey/chrome_test_case.mm

@@ -57,7 +57,8 @@ NSArray* whiteListedMultitaskingTests = @[
   @"testErrorPage",                             // ErrorPageTestCase
   @"testFindInPage",                            // FindInPageTestCase
   @"testDismissFirstRun",                       // FirstRunTestCase
-  @"testLongPDFScroll",                         // FullscreenTestCase
+  // TODO(crbug.com/872788) Failing after move to Xcode 10.
+  // @"testLongPDFScroll",                         // FullscreenTestCase
   @"testDeleteHistory",                         // HistoryUITestCase
   @"testInfobarsDismissOnNavigate",             // InfobarTestCase
   @"testShowJavaScriptAlert",                   // JavaScriptDialogTestCase